Wireless communications networks may be divided into cells, with each base station antenna in the network servicing a cell. Base station antennas generally tilt their beams downwards, towards the mobile handsets carried by users and to minimise energy radiated above the horizon. However, the simplest antenna geometry places radiating elements in a plane parallel to a vertical reflecting ground plane. This causes energy to be radiated equally above and below the horizon.
Various methods of achieving downtilt of the antenna radiation pattern have been proposed. In an antenna array, downtilt may be adjusted by arrangement of phase relationships between radiating elements. Alternatively, the radiation pattern of each radiating element may be tilted, either by physically tilting the radiating element, or by use of parasitic elements.
In US 2005/0001778 the ground plane is divided into a number of “element trays” which are arranged in a staircase structure. Each tray is tilted to aim below the horizon. This leads to an increase in part quantity, cost, assembly time, weight and complexity.
JP 02260804 proposes a circular patch antenna with a pair of parasitic elements mounted above each circular patch. Each parasitic element is a circular patch of the same dimensions as the radiator. Thus, the parasitic elements are of a resonant dimension. The resultant direction of radiation passes through the centre of the parasitic elements. This system would result in a substantial decrease in half power beam width and is therefore not suitable for use in a panel antenna for wireless communications systems.
It would therefore be desirable to provide downtilt in a base station antenna with reduced cost and complexity.